1. Field of the Invention
The invention relates to a machining apparatus for machining a workpiece, to a general-purpose apparatus, e.g., a “machining center”, that performs a variety of different types of machining operations by switching between various machining tools, and to a production line provided with a plurality of machining apparatuses.
2. Description of the Related Art
Conventionally, a production line for automatic transmissions (hereinafter referred to as “A/T” or “A/Ts”) includes a machining line with plural machines for machining various types of workpieces, namely, components of the A/T. This machining line includes a plurality of machining centers (hereinafter referred to as “M/C” or “M/Cs”) that are arranged in a line and a robot that mounts and removes the workpieces to/from the table of each M/C. Further, the same type of machining line is also utilized in production lines for devices and machines other than A/Ts.
An example of a machining line provided with a plurality of M/Cs and a robot is described in Japanese Patent Laid-Open Publication No. 2001-255922 as having three M/Cs positioned in a straight line and a single robot that travels along the line of M/Cs for mounting and removing respective workpieces to/from the tables of the M/Cs.
In the machining line disclosed in Japanese Patent Laid-Open Publication No. 2001-255922, the robot removes an unmachined workpiece from a workpiece carrying device, and following mounting of the unmachined workpiece on a table of a first M/C, the first M/C machines the workpiece. Next, the robot removes the workpiece (the machining of which has been finished at the first M/C) from the table of the first M/C, and carries it to a second M/C that performs the next machining step. The workpiece is then mounted on the table of the second M/C where it is further machined by the second M/C. Then, the robot removes the workpiece (the machining of which has been finished by the second M/C) from the table of the second M/C, and carries it to an nth M/C that performs the next machining step. The workpiece is then mounted on the table of the nth M/C, and the nth M/C performs another machining step. Lastly, the robot removes the workpiece (after completion of machining by the nth M/C) from the table of the nth M/C, and then another workpiece carrying device carries the workpiece away. In this way, the machining processes of the first to nth M/Cs are performed in sequence on the workpiece.
However, with the above-described machining line disclosed in Japanese Patent Laid-Open Publication No. 2001-255922, the robot does not return to the first workpiece carrying device (carrying-in device) until the machining of a given workpiece has been finished by the nth M/C. Accordingly, while a given workpiece for which machining has been completed by the first M/C is being processed by the second M/C, it is not possible to mount another workpiece in the first M/C. As a result, machining of the next workpiece cannot be performed by the first M/C. In addition, similarly, while a given workpiece that has been finished by the second M/C is being further machined by the nth M/C, it is not possible to mount successive workpieces in the first and second M/Cs. Accordingly, machining of the successive workpieces cannot be performed by the first and second M/Cs. Thus, there is substantial wasted time in the operation of this machining line, and the machining operations are not performed efficiently. Thus, a long time is required for the completion of machining of a given number of workpieces.
In order to address these problems, it would be possible to modify the machining operation of the machining line disclosed in Japanese Patent Laid-Open Publication No. 2001-255922 such that, following transfer of a given workpiece that has been finished at the first M/C to the second M/C, the robot moves back to the carrying-in device and removes an unmachined workpiece therefrom, mounts it on the table of the first M/C, and then carries the workpiece, for which machining has been finished at the second M/C, to the nth M/C, and mounts it therein. Following carrying to the nth M/C in the above mentioned manner, the robot could be made to travel back to the first M/C so as to remove the workpiece for which machining has been finished, to carry the workpiece to the table of the second M/C, and to mount it thereon. The robot could then be made to travel back to the carrying-in device and remove another unmachined workpiece therefrom, and to mount this workpiece on the table of the first M/C. In addition, similar robot operational control could be executed when a given workpiece finished at the nth M/C is carried to the carrying-out device by the robot. However, if robot operation control were to be executed in this manner, the robot would be subjected to repeated forward-and-backward movements between the carrying-in device, the first, second and nth M/Cs, and the machined workpiece carrying-out device. Accordingly, there would still be substantial wasted time in the machining operation.
Moreover, the process requires the robot to execute mounting and removal of the given workpieces for each M/C, as a result of which the workpiece mounting and removal operations are complicated. In addition, the robot is required to execute a sequence of operations, namely, mounting the workpiece, removing the workpiece and movement along the M/C line. Accordingly, the robot operation control becomes complicated and cumbersome.
FIG. 7 illustrates a machining line 1 including a predetermined number n (n≧2) of M/Cs arranged in a line, and temporary workpiece stations respectively located between the M/Cs. More specifically, the machining line 1, includes a first M/C 2, a second M/C 3, an nth M/C 4, an unmachined workpiece placement station (hereinafter referred to as “workpiece station”) 6, a first M/C post-machining temporary workpiece station 7, a second M/C pre-machining temporary workpiece station 8, a second M/C post-machining temporary workpiece station 9, an nth M/C pre-machining temporary workpiece station 10, a completed workpiece station 11, a robot 13, and a guide rail 14.
The robot 13 is, for example, a conventional articulated arm robot. As shown in FIG. 7, the robot 13 is provided with a main body 13a and a first arm 13b connected to the main body 13a for horizontal rotation and raising and lowering relative to the main body 13a. A second arm 13d at one end carries a workpiece holder and is telescopically connected to the first arm 13b for retraction and extension relative thereto. Similar to the structure shown in FIG. 4(a) (described hereinafter), the workpiece holder is connected to the second arm 13d so as to allow relative rotation around an axis that is perpendicular to the view in FIG. 7.
Accordingly, the workpiece holder 13c is capable of movement upward and downward, left and right, and forward and backward, within ranges of movement of the first and the second arms 13b and 13d. Further, the workpiece holder 13c is maintained in a substantially horizontal position with movement of the first and second arms 13b and 13d, through use of a conventional mechanism. Of course, the robot 13 is not limited to the above described configuration, and any robot that can be utilized in the machining line 1 and which is capable of mounting and removing the workpiece 5 to/from the respective M/Cs 2, 3 and 4, may be used. The robot 13 is mounted for movement along the guide rail 14 along which each of the M/Cs 2, 3 and 4 is positioned.
Next, the operation of the machining line 1 shown in FIG. 7 will be explained. First, the workpiece 5, is carried to the workpiece station 6 in the vicinity of the first M/C 2 and placed thereon. Then, the main body 13a of the robot 13 is moved to a predetermined position that corresponds with the first M/C 2, and the first and second arms 13b and 13d are moved to retracted positions. Then, the robot 13 is activated and the first arm 13b is appropriately rotated in a horizontal plane and appropriately vertically positioned. Moreover, the second arm 13d is appropriately extended-retracted relative to the first arm 13b. As a result, the workpiece holder 13c is positioned, as shown by the dot-dash line, at the workpiece station 6.
The workpiece holder 13c holds the workpiece 5 at the workpiece station 6, and then the first and second arms 13b and 13d operate to move the workpiece holder 13c to the position indicated by the solid line. At this time, the workpiece 5 held in the workpiece holder 13c is moved to a fixing point 2k on top of a table of the first M/C 2 where it is fixed to the table. Following this, the first and second arms 13b and 13d are retracted back to their original positions.
The workpiece 5 on top of the table of the first M/C 2 is fixed thereto by a clamping device (not shown), and the first M/C 2 is operated to perform a first machining operation on the workpiece 5. When the first machining of the workpiece 5 is finished, the clamping device releases the workpiece 5. Then, both arms 13b and 13d of the robot 13 are operated to grasp the workpiece 5 with the workpiece holder 13c, to remove the workpiece 5 from the table of the first M/C 2, and to then temporarily place the workpiece at the first M/C post-machining temporary workpiece station 7 as indicated by the dot-dash line in FIG. 7. Next, both arms 13b and 13d of the robot 13 are moved back towards the workpiece station 6, and once the workpiece holder portion 13c has grasped the next workpiece 5 at the workpiece station 6, in a similar manner as before, and places it on top of the table of the first M/C 2. Then, the next workpiece 5 is fixed to the table of the N/C 2, and the first machining operation is again executed.
Next, the robot 13 grasps the workpiece 5, for which the first machining has been completed and which has been temporarily placed at the first M/C post-machining temporary workpiece station 7. Then, the main body 13a of the robot 13 moves toward the second M/C 3 while guided by the guide rail 14, and the workpiece 5, for which the first machining has been completed, is temporarily placed on the second M/C pre-machining temporary workpiece station 8, as shown by the dot-dash line. The robot 13 then stops at a predetermined position that corresponds with the second M/C 3 (the position indicated by the solid line in the middle of FIG. 7). Next, in a similar manner as before, the robot 13 grasps the workpiece 5, for which the first machining has been finished and which is at the second M/C pre-machining temporary workpiece station 8, and places the workpiece 5 on the table of the second M/C 3.
As before, the workpiece 5, for which the first machining has been finished is fixed to the table of the second M/C 2, and then a second machining is performed. When the second machining is finished by the second M/C 3, the robot 13 takes the workpiece 5 and temporarily places it on the second M/C post-machining temporary workpiece station 9. Then, the robot 13 moves again to the predetermined position (the solid line shown to the left-hand side of FIG. 7) corresponding to the first M/C 2. Then, as before, the next workpiece 5 for which the first machining has been finished is taken and temporarily placed on the first M/C post-machining temporary workpiece station 7, and yet another workpiece 5 is taken from the workpiece station 6 and placed on the table of the first M/C 2. Following this, the robot 13 moves and takes the workpiece 5, for which the second machining has been finished and which is on the second M/C post-machining temporary workpiece station 9, and temporarily places it on the nth M/C pre-machining temporary workpiece station 10.
Following this, in the manner described above, the robot 13 continues to execute the transport, mounting and removal operations with respect to each of the M/Cs 2, 3 and 4, and the M/Cs 2, 3 and 4 repeatedly perform their respective machining operations. When the nth machining by the nth M/C 4 is finished, the robot 13 takes the workpiece 5 from the nth M/C 4, and places it on the completed workpiece station 11, as a machined part 12. This machined part 12 is then carried to the next work station by a suitable device. It should be noted that it is possible to integrate the respective neighboring M/C post-machining temporary workpiece stations and the M/C pre-machining temporary workpiece stations (for example, those indicated by reference numerals 7 and 8) into a single common workpiece temporary placement point.
In the mounting and removal operations for of the workpiece 5 executed by each M/C, it is sufficient for the robot 13 to control operation of the arms 13b and 13d, and there is no need for the robot 13 to control movement of its main body 13a. Accordingly, the robot control is made correspondingly simpler.
However, even with the machining line 1 shown in FIG. 7, mounting and removal of the workpiece 5 by the robot 13 must be executed for each M/C, and thus the mounting and removal operations of the workpiece 5 are complicated.
Moreover, when the machining of the workpiece 5 by one M/C is finished, the robot 13 takes the workpiece 5 and temporarily places it at a temporary placement station. Following this, the robot 13 moves it to the neighboring M/C which is next in line in the upstream direction, and when the machining of this M/C is finished, temporarily places the workpiece 5 at the respective temporary placement station. The robot 13 progressively moves in sequence, in the processing flow upstream direction, while executing similar operations. However, after a new workpiece 5 is mounted in the first M/C 2, the robot 13 must travel to the M/C of the machining line 1 at which the workpiece 5 that has progressed furthest in the machining is located, i.e., where the far-end workpiece 5 is located. When this far-end workpiece 5 has been machined by the nth M/C 4, the robot 13 must travel to the nth M/C 4. Accordingly, the robot 13 must repeatedly move forward and backward and, thus as with the conventional apparatus, there is substantial wasted time in the machining operation, making the machining operation less efficient.
Further, because it is necessary to provide the temporary placement points for the workpiece 5 between each M/C, these temporary placement points must be taken into account in design of the machining line 1, unavoidably making it larger.